US2208507A - Process for sweetening hydrocarbon oils - Google Patents

Description

Patented July 16, 1940 UNITED STATES- PATENT OFFICE raocass ron swnn'rcmnc immo- ARBON OILS No Drawing. Application November 3, 1939,

Serial No. 302,774

9 Claims.

Our invention relates to the sweetening of hydrocarbon oils and more particularly has reference to improvements in the conventional doctor sulfur and an aqueous alkaline solution of sodium plumbite, known as the doctor solution." The plumbite solution effects a chemical reaction between the mercaptans and the elementary sulfur, resulting in the conversion of the mercaptans to dialkyl disulfides and also into some trisulfide, while the sulfur is converted mainly into sulfides, polysulfides, thiosulfates, etc. Y

In practicing the conventional doctor treatment, an excess of elementary sulfur is used to bring about a break, a term used in the art to indicate the settling or subsidence point in the doctor treatment. That is to say, the amount of free sulfur used is in excess of the theoretical quantity required to convert the mercaptans into disulfides and other innocuous compounds, the excess serving to induce the "break in the treatment. Such use of elementary sulfur to effect settling or subsidence results in the incorporation of sulfur into the distillate, with its attendant objections. Among these objections, in the case of gasoline, are poor inhibitor and tetraethyl lead susceptibility, lowered anti-knock value, increased corrosive'action on metals, poor color and odor stability, and increased tendency to form gum.

Although doctor treatment in its many variations is well understood in the art, it may be well to emphasize, by a suitable reference, the circumstances and conditions attending, a break and the difliculty of coagulating the colloidal black precipitate.

Doctor plants differ in the way in which doctor solution and sulfur are mixed with the gasoline and the length of time they remain in contact. It is common practice to add the sulfur in gasoline solution before, at the same time as, or after the gasoline and doctor solutions are mixed. The mixing may be done by orifice plates, baflied pipes, pipes with right-angle bends, or mechanical mixing devices, and mixingtime may vary from a few seconds to several minutes.

When sulfur is added to a mixture of gasoline and doctor solution, the oil becomes orangered in color; after a longer or shorter time, depending on the gasoline and the amount of sulfur added, the break takes place, when the color disappears and a red-brown to black precipitate,

usually called lead sulfide, forms and settles.

In different plants, the break may be produced as the gasoline leaves the mixers or it may not occur until after the gasoline has entered the settling drum. If a plant has adequate mixing (the proper time of mixing will depend on the type of gasoline and somewhat on the degree of sourness), the gasoline may be allowed to break as it leaves the mixers, and the amount of sulfur required to do this will not be so great as to harm inhibitor susceptibility. However, if a plant has little mixing equipment (a common installation is three mixing nozzles in about six feet of line, which for most gasoline is much less mixing than is desirable), a break cannot be obtained in the mixers without using a considerable excess of sulfur, with consequent detriment to the inhibitor effectiveness. If, however, the break in such plants occurs in the first settler from three to fifteen minutes after the gasoline leaves the mixers, the results from an inhibitor standpoint will usually be satisfactory. But when the break oc-' curs in the settler, the gasoline being no longer in contact with doctor solution, it tends to produce a finer precipitate, settling more slowly than when the gasoline is broken out while still in contact with doctor solution. As plants deficient in mixing equipment are also often lacking in settling capacity, the treater in such cases faces a serious dilemma. If he uses excess sulfur, his gasoline settles well but inhibitor suscepti-' bility is poor; if sulfur is kept down, the gasoline breaks and settles slowly and lead sulfide leaves the plant suspended in the gasoline. (Industrial & Engineering Chemistry, vol. 30, No. 11, Nov. 1938, p. 1276.)

Thus, in actual practice, the present trend has been to continue to use sulfur as a break inducer,

insofar that no universal and economic solution of the problem has been heretofore available. Some effort has been made to solve the problem by subsequent washing with aqueous solution, but

- this has resulted in attendant loss of expensive any attempt has been made to apply such process in instances where the amount of elementary sulfur represented only theoretical quantities and which would necessitate that the simple fatty materials, such as soap, be relied upon solely as the break inducer.

We have now found that drastically oxidized ricinoleic acid bodies possess the property of inducing a break in the doctor treatment and our invention involves their use, in the sweetening of sour oils by means of plumbite solution and elementary sulfur, to effect the'fsettling or subsidence in the known sweetening process.

More specifically, break inducersof our invention are oxidized oils obtained fronrcastor oil, ricinoleic acid, and various derivatives of ricinoleic acid of the kind hereinafter described,.

place in the presence or absence of a catalyst.

Thecatalyst may be of a metallic type, such as lead ricinoleate, cobalt ricinoleate, manganese ricinoleate, etc.; or itmay be of the organic type which produces peroxide such as alpha pinene, linseed oil, etc. Oxidation may take place at atmospheric pressure or super-atmospheric pressure, i. e., pressures up to or including 200 pounds gauge pressure, and at any temperature slightly above the boiling point of water, for instance, 120 0., up to any temperature which does not produce undue decomposition by pyrolytic reacion.

The time of blowing may be fairly brief, for example, 8-10 hours; or it may be quite extensive,

for instance, as long as 10-12-14 days, the longer time periods being employed generally when the temperature is just slightly above the boiling point of water and when oxidation is with air at atmospheric pressure. I

Mild oxidation, i. e., oxidation as exemplified by the exposure of a film of castor oil to air for an extended period of time, such as weeks or even months (see Chemical Technology and Analysis of Oils, Fats, and Waxes, by Lewkowitsch,

sixth edition, volume 2, page 406) produces relatively small modifications of certain important indices, such as the iodine value, the acetyl value, and the saponification value. If drastic oxidation takes place, either by continued mild oxidation or by more vigorous oxidation from the very beginning of the .reaction as induced by either a higher reactiontemperature or the presence of a catalyst, then there is obtained an oxidized oil having characteristics which clearly indicate that drastic oxidation has taken place. These indices of drastic oxidation are a relatively low iodine value,- such as 70 or less, and may be as low as 40 or thereabouts; a saponification value of 215 to 283 or thereabouts; an acetyl value of approximately 160-200; an increased viscosity such that the material may be hardly mobile at ordinary temperatures; a specific gravity of almost one or a trifle over one at times; an increased refractive index; and, in the absence of other coloring matter, a yellow to deep orange'color. The color at times may be a questionable index, since some oxidized castor oils are bleached to make them particularly adaptable for use as plasticizers in light colored reslnold bodies.

Drastically oxidized castor oil can be prepared bywell known methods or such products can be purchased in the open market under various trade names, such as "blown castor oil, blended castor 1." blended bodied castor oil, processedcastor oil, oxidized castor oil," "heavy castor oil,"

"viscous castor oil, etc. These various trade names appear to be applied to drastically oxidized castor oils which difi'er merely in degree but not in kind.

The color of these oils is still pale or light 5 colored in comparison with the oil from which they have been derived. Usually they are fairly transparent particularly in reasonably thin layers, for instance, an inch or less. Such oils represent greater or lesser degrees of partial l0 oxidation in the sense that there is a drastic change in comparison with the change that takes place when a film of castor oil is exposed to air.

For sake of difierentiatiom'oils of the kind previously described will be referredto as pale 15 blown, drastically oxidized castor oils; and the same terminology is intended to apply to all other ricinoleic bodies of the kind hereinafter described.

In addition to pale blown, drastically oxidized castor oil, there is also another type of the kind 20 described in U. S. Patent 2,023,979, to Stehr, December 10, 1935. The product described in said Stehr patent is characterized by the fact that drastic oxidation is continued past the stage where a pale blown oil is obtained and where, as 25 a matter of fact, a super-oxidized product of almost semi-livery consistency is obtained.

Such products are usually much darker in color than the pale blown castor oils,. for the reason that certain side reactions occur with the 30 formation of dark colored by-products; and as a result, the transparency of the oil has greatly decreased or disappeared, and it is apt to be opaque in nature.

We have found that such super-oxidized castor oil or ricinoleic body is just as effective a break inducer as the pale blown oils in which drastic oxidationhas not proceeded to as great a degree.

It is obvious that oxidized fatty acids, such as oxidized ricinoleic acid, diricinoleicacid, poly- 40 ricinoleic acid, and the like, may be considered as the equivalent of the corresponding oxidized castor oil and may be employed just as suitably. Such fatty acid may be oxidized in a manner to produce a moderate change and'thus give the 45 equivalent of a pale blown oil; or it may be superoxidized in the manner described in the aforementioned Stehr patent. Similarly, ricinoleic acid or castor oil fatty acids may be heated so as to cause polymerization to take. place prior to 50 the oxidation step. In other words, oxidation need not be limited to unpolymerized ricinoleic acid or unpolymerized' castor oil fatty acids, but may be employed in conjunction with heated or polymerized ricinoleic acid or heated or polymer- 55 ized castor oil fatty acids.

It is customary to classify generically. these materials of the kind above described as ricinoleic acid bodies.

, Our preferred break inducer is a pale blown 60 castor oil of the following characteristics:

' It is obvious that in the use of the blown oils in the sweetening process, reaction must take place to a, greater or lesser degree with the alkali of the doctor solution, so as to result in a saponifi aaoasov diamylamine, triamylamine, diethanolamine, triethanolamine, morpholine, etc. Needless to say, any acidity present could be eliminated, if desired, by means other than saponiflcation; i. e., carboxy groups, if present, could be converted by conventional processes into esters such as the methyl ester, ethyl ester, propyl ester, and esters of hydroxylated amines in which the hydroxylated amines act as alcohols.

In some instances, the quality of the blown oil can be improved by continuing the heating of the oil for some time after the oxidation has ceased, possibly even at a somewhathigher temperature than was employed during oxidation. Such added step induces further polymerization or some other reaction.

The compounds herein disclosed are preferably used as the "sole break inducer for the doctor treatment, in which event the quantity of elementary sulfur employed in the doctor treatment is notin excess of the theoretical amount required to convert the mercaptans. In this preferred operation, where no appreciable excess of sulfur is used in the doctor treatment, there is effected a faster break than can be obtained by means of other break inducers and frequently a break is effected where one might not be otherwise obtainable. Additionally, there is recovered a distillate which is free of excess sulfur, an important' advantage as has already been indicated.

However, the invention is not limited to the use of the organic compounds referred to as the sole break inducer but they may be employed in conjunction with other substances having a like property, such as elementary sulfur. In operation of this type, a small excess of sulfur would be used in the doctor treatment, the excess functioning with the compounds of this invention to bring about the desired break in the treatment. The advantages of such operation are that relatively little sulfur is required, the break is induced very rapidly, and frequently a break is effected where one cannot be obtained at all by means of sulfur alone.

. As to the preferred operation above indicated.

it will be observed that the doctor treatment differs from that heretofore employed in that the quantity of elementary sulfur added is only the theoretical amount'based on stoichiometrical calculations, or other comparable test, to convert mercaptans to disulfides and other innocuous compounds, there being present during the treatsulfur present, this elementary sulfur can be detected by the addition of butyl mercaptan or the like, followed by a doctor test on the admixture. A large excess may be indicated by the less sensitive copper strip test.

The butyl mercaptan test, referred to above, is commonly used in'a qualitative manner to detect excess elementary sulfur. This test is described in the Universal Oil Products Co. Bulletin No. 22, p. 15, as follows: I

In doctor sweetening, the most important factor in securing inhibitor effectiveness, is to use the smallest possible amount of sulfur. Sulfur addition may be controlled by testing with mer-,

cury or butyl mercaptan. In making the butyl mercaptan test, a sample of gasoline drawn from the doctor plant after it has left the mixers is allowed to stand until the lead sulfide has settled, and .33 cc. filtered into a 4 ounce oil sample bottle. 20 'cc. of a l to 1,400 solution of butyl mercaptan is added and 10 cc. of doctor solution. The mixture is shaken ,for seconds and observed. The sample should be green-yellow. It will slowly become opaque but should remain yellow in color even if observed for 30 minutes. If it turns orange or brown, excess sulfur has been used, and on addition of inhibitor the gasoline will have lower induction period and higher copper dish gum than would have resulted had less sulfur been used.

The chemistry of the reactions which enter into doctor sweetening is rather complex and not completely understood. However, it is common practice, for the purpose of calculating the amount of sulfur necessary, to use the following reaction as being representative:

With distillates where these reactions take place, the theoretical sulfur requirement may be calculated by use of the above equations and the known-original mercaptan content of the distillate. However, for all practical purposes, the butyl mercaptan test, previously described, may

be used as a test for whether or not excess sulfur has been used. Accordingly, the term negative to the butyl mercaptan test, as applied to sweetened distillates, is used herein to mean that a distillate has been sweetened'with the theoretical amount -of sulfur, or that the minimum amount of sulfur necessary for completion of the sweetening reaction has been employed. The reason for this is that the butyl mercaptan test may be made more easily and more quickly than a determination of the actual course or nature ofthe sweetening reactions.

As is understood. of course, if hydrogen sulfide is present, allowance must be made for the amount of lead required to remove such sulfide. However, this is not apt to be a factor requiring consideration, due to usual preliminary removal of hydrogen sulfide.

In view of what has been said-previously, it is obvious that the satisfactory application of the doctor treatment must involve a rapid and complete separation of lead sulfide and associated insoluble material, as soon as the mercaptans are converted into disulfldes or other more innocuous compounds. Although the above reactions indicate only precipitation of lead sulfide, it has been found that in reality a precipitate may contain a comparatively small amount of lead sulfide;

' and there may also be present various complex 7 tion, and particularly to give subsidence or settling of the black precipitate, is not so definite. As a matter of common practice, sulfur is added in the conventional doctor treatment for two distinct purposes of converting mercaptans and inducing the break; and these two purposes must be fully appreciated in order to understand the benefit obtained by applying the improved procedure-which constitutes our present invention,

particularly in its preferable form, 1. e., where the complex organic compounds herein described are used as the sole break inducer, with only the theoretical amount of sulfur to convert mercaptans or togive a negative butyl mercaptan test.

It has heretofore been proposed to employ water soluble soaps to effect the break in doctor treatment, the soaps being utilized in ratios of 1 to 2500 or 1 to 7500. At such ratios, the common soaps are often ineffective and hence there is the tendency to employ just as much sulfur as if no soap had been added. In contradistinction to the common soaps heretofore contemplated, the break inducers of the present invention are invariably effective and invariably enable a marked reduction in the amount of sulfur needed in the doctor treatment, even to the extent, as in the preferred embodiment already described, of limiting the sulfur to the theoretical amount necessary for converting the mercaptans into innocuous compounds.

. The-break inducers of this invention need be used in only very minute quantities, for example, in ratios varying from 1 to 5000 or 1 to 7500 or even 1 to 75,000, based on recovered or sweetened gasoline or other distillate treated. To the extent that our improved break inducers possess the property of forming oil-in-water emulsions, it should be observed that they are employed in such insignificant quantities that they do not exhibit any detectable or appreciable emulsifying action.

Although our invention can be applied to any the herein disclosed organic compounds are used as sole break inducers. It is obvious, however, that those skilled in the art and acquainted with such procedure could readily modify the conventional doctor treatment in which elementary sulfur is used as a break inducer, so as to reduce the amount of sulfur employed, and offset that I reduction by suitable quantities of the break inducers of this invention. I

In a continuous doctor sweetening plant, the organic break inducer is added continuously to the stream of sour distillate prior to its admixture with doctor solution and sulfur. When the break inducer is a liquid, this is conveniently done by means of a small injector pump adjusted to deliver the break inducer in some definite, desired amount, usually within the limits of one part per 7500 to 75,000 parts of gasoline. After the introduction of break inducer has begun, the amount of sulfur added to the distillate, or to the mixture of distillate and doctor solution, is decreased to the theoretical amount.

- In batch system doctor sweetening plants, the required amount of break inducer is introduced into the sour distillate and mixed thoroughly before the treatment with doctor solution and sulfur. In this case, also, the amount of sulfur used is reduced to the theoretical amount.

Sometimes better results are obtained if the break inducer is added to the doctor solution or to thedistillate after the latter has been mixed with doctor solution and sulfur. Regardless of the point of introduction of the break inducer, however, the amount of sulfur required for completion of the sweetening reactions and subsidence of the black precipitate is reduced to, or

v nearly to, the theoretical amount.

The doctor solution used for sweetening is generally regenerated after each use and employed for sweetening further amounts of sour distillate. Where the break inducer has been added to the doctor solution, its activity may persist thru' one or more regenerations, but eventually further amounts will have to be added. The number of volumes of distillate sweetened per volume of break inducer used in the doctor solution usually will be more than 7500, and the ratio of break inducer mayaverage one part to 25,000 parts sweetened distillate.

In order to indicate the effectiveness of the present process, attention is directed to thefollowing table. The gasoline employed in the present instance was obtained from East Texas crude petroleum. The figures given refer to tests variation of the conventional doctor treatment made with-100 gram portions of gasoline:

Ami J3 B...

I yl mertfi '3; HM *ndmwd ggggm tit? 33mm mm (t treated 3. 0 3. 0 None 0 None obtained.. 3.0 4.0 do 0 None obtain 3.0 5.0 do 0 Negatlve.... lositivenfl- 3. 0 3. 0 Sodium steer-ate ,0. 0102 None obtained. 3.0 4.0 do 0.0M air Negative.... Positive..." 3. 0 3. 0 Sodium oleate 0. 000a None obtain 3.0 4.0 do 0.000s Poor, slow Negative-.. Poaitive 3. 0 3. 0 Sodium resinate 0. 0002 None obtaine 3.0 4.0 --do 0.0002 sir Negative.... Positive 3. 0 3. 0 Castile scapm. 0.0002 None obtain 3 0 4 0 d 0.0112 air Negati Postiti 3. 0 3. 0 Pale blown castor oil 0.0001 Goof .-do Negative... 3. 0 3. 0 Blown castor oil acids 0. 0001 c n .do Do. 3.0 3.0 Super-oxidized castor 00.... 0.0001 r a do Do.

in a manner whichis most convenient under the specific conditions surrounding the particular operation, for purposes of brevity, we will describe only the preferable form of procedure, 1. e., where Examination of the above table emphasizes the numerous salient points previously discussed. For instance, reference is made to those tests in the above table which are concerned with the use of the common, rather simple, type of break inducer, to wit, materials such as sodium stearate, sodium oleate, castile soap, sodium resinate and the like.

Furthermore attention is directed to the first three tests which indicate the results obtained when sulfur alone is used as thebreak inducer. It is to be noted that in the tests as conducted, it was necessary to use three milligrams of sulfur in order to complete the chemical reactions. n the other hand, the addition of 33% excess of sulfur, i. e., the use of 4 milligrams of elementary sulfur, did not ,give a break. However, when the amount of sulfur used was increased to 5 milligrams, i. e., a 66%% excess, then a perfectly satisfactory break was'obtain'ed. Obviously such excess of elementary sulfur resulted in a positive butyl mercaptan test. When an effort was made to substitute the common soap type of break inducer for elementary sulfur, it was found that its use, in amount equivalent to times the amount of sulfur required for break induction, did not give satisfactory results. For instance, when the 2 milligram excess of elementary sulfur was replaced by milligrams of sodium stearate, a good break was not obtained. This same condition prevailed when a similaramount of sodium oleate or sodium resinate or castile soap was employed. When there was added only the amount of elementary sulfur required to complete the chemical reaction and it was attempted to depend on the addition of sodium stearate, sodium oleate, castile soap or sodium resinate, as sole break inducers, a satisfactory break was not obtained even when these compounds were employed in a ratio of 1 to 5000. In comparison to the results above indicated, attention is directed to the results obtained when employing the break inducers herein contemplated for use in the doctor treatment.

It is to be noted that the oxidized castor oil and acids were used in a ratio of 1 to 10,000 and in each case, an excellent break was obtained even though there was no sulfur available for break induction, or to say it in another way, when the amount of sulfur employed was-only sufiicient to complete the chemical reactions involved. In each instance, sincethere was no excess sulfur employed, the butyl mercaptan test obviously has to be negative. Since the butyl mercaptan test had to be negative, it followed that the gasoline was of a type which was free from certain inherently objectionable qualities which are common when there is an excess of elementary sulfur present, or when the gasoline gives a positive butyl mercaptan test. In each instance, the break obtained was the Madmanterized as being good," i. e., appeared to be satisfactory under any condition of plant operation which one would ordinarily employ.

We have previously indicated that the amount of added break inducer may be as low as one part in 75,000-parts of the oil being sweetened. In practice, however, the amolmt of break induceractually present in the oil may be even less than this during certain phases of the process. For example, in an operation involving recirculation of doctor solution, the ratio of break inducer Therefore, it is to be understood that the hereto fore mentioned ratio of 1-75,000 is not the upper limit of effectiveness, particularly in a recirculation process.

It will be further understood that, instead of employing a single break inducer of the kind herein disclosed, a mixture of two or more of them may be used, if desired. Indeed, the process of manufacture may result in the production of a mixture of a number of break-inducing compounds rather than a single compound in a technically or chemically pure state. Moreover, a break inducer of this invention may be employed in admixture with other types of break inducers for which we have filed separate applications Frequently, the compounds of this invention have beneficial effects in addition to bringing about rapid subsidence. For example, as a result of their use, the amount of black strap or feathery material appearing at interfacial surfaces may be greatly diminished or entirely eliminated.

It is to beunderstood that the detailed disclosures herein are for illustrative purposes only and are not to be considered as limitations on the invention, inasmuch as various modifications within the scope of the appended claims will be apparent to those skilled in the art.

Having described our invention, we claim:

1. In' the sweetening of sour hydrocarbon oils by treatment with doctor solution and elementary sulfur, the method of inducing a break in the doctor treatment which comprises adding to the oil a relatively small amount of a drastically oxi dized ricinoleicacid body.

2. A method for sweetening hydrocarbon oils containing mercaptans which comprises treating the oil with doctor solution and suflicient elementary sulfur to convert the mercaptans into innocuous compounds, and inducing a break in said treatment by the addition of a drastically oxidized ricinoleic acid body.

3. A method for sweetening hydrocarbon oils containing mercaptans which comprises treating the oil with doctor solution and a quantity of elementary sulfur not appreciably in excess of the theoretical amount required to convert the mercaptans into innocuous compounds, and inducing a break in said treatment by the addition of a drastically oxidized ricinoleic acid body.

4. A method for sweetening hydrocarbon oils -containing mercaptans which comprises converting the mercaptans into innocuous compounds by treatment of the oil with alkaline plumbite solution and elementary sulfur, the amount of sulfur being insufficient to render the oil'positive to the butyl mercaptan test and insufficient to effect settling or subsidence, and inducing a break in said treatment by adding a drastically oxidiz ricinoleic acid body.

5. In the sweetening of sour hydrocarbon oils by treatment with doctor solution and elementary sulfur, the method of inducing a break in the doctor treatment which comprises adding to by treatment with doctor solution and elementary sulfur, the improvement which comprises facilitating the break in said treatment by the addition'of a drastically oxidized castor oil fatty acid.

CHARLES M. BLAIR, JR. IRA S. BOYDSTUN.v